Unilateral contact induced blade/casing vibratory interactions in impellers: Analysis for flexible casings with friction and abradable coating

Journal of Sound and Vibration

Batailly

2019

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Blade/casing rubbing interactions in aircraft engines: Numerical benchmark and design guidelines based on NASA rotor 37. Journal of Sound and Vibration, Elsevier, 2019, 460, pp.Abstract In order to improve the efficiency of aircraft engines, the reduction of clearances between blade tips and their surrounding casing is one avenue manufacturers consider to lower aerodynamic losses. This reduction increases the risk of blade tip/casing contact interactions under nominal operating conditions. Designers need tools to accurately predict subsequent nonlinear vibrations. Engineers and researchers have developed a variety of sophisticated numerical models to predict blades' responses. These models are related to distinct frameworks (time/frequency domain) and various solution algorithms (explicit/implicit time integration schemes, penalty/Lagrange multiplier contact treatment...) which calls for comparative analyses. However, published results are often limited for the sake of confidentiality thus preventing any detailed confrontation. While qualitative understanding can be gained from simplified academic models, full scale models are needed to predict complex interactions in a realistic manner. In this context, this paper proposes a benchmark featuring detailed simulations and analyses of a full 3D finite element model based on the open NASA rotor 37 compressor blade to facilitate reproducibility and collaboration across the research community. NASA rotor 37, a compressor stage widely used as a test case in aerodynamic simulations and validations, has the advantage of presenting a realistic blade geometry. The geometry of the blade is built from publicly available reports. The paper provides details on the geometry, the numerical model and the results to allow an easy use of this model across the fields of structural dynamics. Two contact scenarios are investigated: one with direct contact against the casing, and one with abradable material deposited on the casing to mitigate contact severity through wear. The nonlinear vibration response of the blade is simulated in the time domain. It is evidenced that the addition of the abradable material decreases the amplitude of vibration for most of the angular speeds investigated. However, new interactions appear for some angular speeds. The obtained results are consistent with previous simulations on industrial geometries. Based on works showing improved aerodynamic performances when the blade is tilted, a total of seven geometries are investigated: the reference blade, with a straight vertical stacking line similar to the original rotor 37, two forward-leaned blades, two backward-swept blades and two full forward chordwise swept blades. The sweep and lean variations are shown to have a dramatic impact on the vibration response: the backward sweep results in an increased blade's robustness to contact events and the full forward chordwise sweep in a reduced robustness, while the forward lean leads to a robustness similar to the reference blade. RésuméLa réduction des jeux au...

Section: Introductionmentioning

confidence: 99%

Blade/casing rubbing interactions in aircraft engines: Numerical benchmark and design guidelines based on NASA rotor 37

Piollet

Journal of Sound and Vibration

Batailly

2019

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“…Previous work carried out with this methodology usually involved a perfectly rigid casing in order to focus on the blade vibration response. This numerical strategy is here extended to segmented flexible stator components building on previous developments presented in [37] for full 360 • casings.…”

Section: Numerical Strategymentioning

confidence: 99%

“…Managing contact between the blades and the shroud segment requires a continuous definition of the normal vector to the contact surface as the blades rotate. This prevents a definition of the normal vector that would rely on finite elements [37]. For this reason, a bi-cubic B-spline surface is computed over the shroud segment contact surface.…”

Section: Shroud Segmentmentioning

confidence: 99%

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Experimental and numerical characterization of a ceramic matrix composite shroud segment under impact loading

Journal of Sound and Vibration

Tableau

Lavazec

et al. 2020

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This work focuses on the experimental and numerical characterization of stress levels within a shroud segment made of ceramic matrix composite (CMC) material undergoing repeated blade contacts. The dedicated experimental setup consists in a rotating disk with three notched mock blades that impact the shroud segment as they rotate. The underplatform on which the shroud is fixed progressively gets closer to the blades, so that the abradable layer deposited onto the shroud is progressively worn out from a blade revolution to another. Four sensors, located under the shroud segment, are used to record forces during the experiments. Different blade/shroud relative positions are tested, in such a way that impacts may occur at distinct locations. In addition to the experimental tests, a numerical model is built based on both reduced order models of the blade and the shroud segment, in order to numerically predict the forces at the four sensors. This numerical model is first calibrated based on a single reference test case to retrieve the same force magnitude at each sensor. Then, the other tests are simulated using the calibrated model. Predicted contact forces are in good agreement with experimental data, which validates the numerical model. Finally, simulations are carried out considering engine-like conditions, which could not be reproduced using the experimental test bench. The influence of several parameters (radial velocity, impact location, number of blades in contact and angular speed) is analyzed in detail.

“…Such hypothesis is commonly accepted when investigating low-or high-pressure compressor stages. For that reason, numerical simulations of two types of rotor/stator interactions namely (1) rubbing phenomena [4,5,6] and, (2) modal interaction events [7,8] have been conducted without accounting for gyroscopic effects. A third type of rotor/stator interactions due to structural contacts is related to the occurence of orbital motions of an aircraft engine fan stage around its axis of rotation.…”

Section: Introductionmentioning

confidence: 99%

Towards Full 3D Numerical Simulation of Whirl Motions Stemming From Unilateral Contact Constraints in Aircraft Engines

Jérémy

Volume 7B: Structures and Dynamics

Parent

et al. 2017

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The reduction of nominal clearances between a rotating bladed-disk and its surrounding casing yields a very significant increase of the overall engine efficiency. However, the smaller the clearances, the higher the risk of structural contacts between static and rotating components that may lead to hazardous interaction phenomena. In particular, at the fan stage of an aircraft engine, impacts between the rotating bladed-disk and the casing may generate forward or backward whirl motions induced by the precession of the shaft axis of rotation. In such specific configuration, an accurate modeling of interaction phenomena requires to account for both centrifugal and gyroscopic effects on the rotor. This contribution addresses the development of efficient reduced-order models of industrial finite element models embedding both centrifugal and gyroscopic effects. Proposed developments are validated on an academic model and are then applied on the finite element model of an aircraft engine fan stage. Results obtained with the academic model underline that the impact of gyroscopic effects on the rotor's dynamics is essentially related to the frequency split of 1-nodal diameter free-vibration modes of the first modal family. Results presented on the industrial finite element models are limited to a few case studies as a proof-of-concept.